`rustfix`: Fix Windows tests

[ehuss]

For some reason, the parse_and_replace test of rustfix is disabled on Windows. I don't know why, but it would be nice for someone to investigate and fix that.

[tompscanlan]

After removing the #![cfg(not(windows))] on line 2, tests will run on win11 powershell. 1 test passes, one test is ignored. Ignored test requires a "custom rustc build" but I'm not sure what that would entail and don't see it in cursory docs scan.

This may be another case like #13034... fix it and keep an eye out for flaky tests.